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Bureau of Mines Information Circular/1987 



Reducing Dust Exposure of Workers 
During Bag Stacking in Enclosed Vehicles 

By Andrew B. Cecala, Anthony Covelli, and Edward D. Thimons 




UNITED STATES DEPARTMENT OF THE INTERIOR 




Information Circular 9148 



Reducing Dust Exposure of Workers 
During Bag Stacking in Enclosed Vehicles 

By Andrew B. Cecala, Anthony Covelli, and Edward D. Thimons 




UNITED STATES DEPARTMENT OF THE INTERIOR 
Donald Paul Hodel, Secretary 

BUREAU OF MINES 

David S. Brown, Acting Director 





Library of Congress Cataloging in Publication Data: 



Cecala, Andrew B. 

Reducing dust exposure of workers during bag stacking in enclosed 
vehicles. 

(Information circular ; 9148). 

Supt. of Docs, no.: I 28.27: 9148. 

1. Loading and unloading- Safety measures. 2. Dust- Removal. I. Covelli, Anthony. II. 
Thimons, Edward D. III. Title. IV. Series: Information circular (United States. Bureau of 
Mines) ; 9148. 



TN295.U4 [TS180.5] 622 s 



[699'.00289] 87-600118 



CONTENT 



Page 



Abstract • 1 

Introduction 2 

Laboratory-scale testing 3 

Laboratory-scale results 5 

Field testing 6 

Discussion 11 

Cost considerations 12 

Conclusions 12 

Appendix. — Curtain evaluation 13 

ILLUSTRATIONS 

1. Product leakage from bag valve while on conveyor 2 

2. Laboratory test setup 4 

3. Fan directions and location used for blowing system tests 5 

A. Dust monitoring locations used for field evaluation 7 

5. Ventilation system used for test 2 8 

6. Ventilation system used for test 3 9 

TABLES 

1. Average concentration from four sampling locations during laboratory 

testing 6 

2. Dust reductions of field testing exhaust ventilation system 10 

A-l. Effect of blowing ventilation system with and without curtain 13 





UNIT OF 


MEASURE 


ABBREVIATIONS USED 


IN THIS REPORT 


cfm 


cubic foot 


per 


minute 


min 


minute 


ft 


foot 








mg/m- 5 


milligram per cubic meter 


hp 


horsepower 








mm 


millimeter 


in 


inch 








pet 


percent 


lb 


pound 








ppm 


part per million 



REDUCING DUST EXPOSURE OF WORKERS DURING BAG STACKING 

IN ENCLOSED VEHICLES 

By Andrew B. Cecala, 1 Anthony Covelli, 2 and Edward D. Thimons 3 



ABSTRACT 

The Bureau of Mines has evaluated a number of ventilation systems for 
potential application in lowering the dust exposure of workers who stack 
bags of mineral product material in enclosed vehicles. Workers who 
stack these bags in enclosed vehicles usually have the highest dust ex- 
posure among all workers in processing plants. This is because dust 
liberated while the vehicle is being loaded has no means of exiting the 
vehicle or being diluted with fresh air and thus, dust concentrations 
increase to substantial levels. Laboratory-scale testing was performed 
in a railcar to compare the effectiveness of a number of different ven- 
tilation systems in reducing the bag stacker's dust exposure. The most 
effective system was taken into the field to optimize its performance. 
The final and recommended system exhausted about 2,000 cfm through 
10-ft-long, 12-in-diam fiberglass tubing located 3.5 ft past the slinger 
at a 6.5-ft height so as to not interfere with the bag stacker's job. A 
6-in-diam tube exhausted approxmately 300 cfm at the snake conveyor- 
slinger transfer point to capture the dust generated there. With this 
system, dust reductions in and around the bag stacker ranged between 65 
and 95 pet when loading both 50- and 100-lb bags of product into rail- 
cars and trailer trucks. 



1 

'Mining engineer. 

^Mining engineer technician. 

■^Supervisory physical scientist. 

Pittsburgh Research Center, Bureau of Mines, Pittsburgh PA, 



INTRODUCTION 



This report describes work the Bureau 
of Mines performed to determine a cost- 
effective system for ventilating enclosed 
vehicles as they exist today. Laborato- 
ry-scale testing was performed to deter- 
mine the most effective system. This 
system was then tested at a mineral pro- 
cessing plant to optimize the technique 
in a working environment and to determine 
its effectiveness in lowering dust con- 
centrations in enclosed vehicles during 
loading of bagged mineral product 
material. 

Many mineral products are packaged in 
50- or 100-lb paper bags. These bags are 



shipped to the customer on pallets, ei- 
ther in railcars or trailer trucks. Bags 
are either loaded by full pallets using a 
forklift, or directly by workers inside 
the vehicle, using a snake conveyor. The 
latter case is discussed in this report. 
Loading bags directly into enclosed vehi- 
cles is advantageous because it elimi- 
nates the forklift and operator. Howev- 
er, it is disadvantageous from a health 
standpoint because of the dust exposure 
to the stackers. 

With direct loading, the bags travel 
down a flexible snake conveyor before 
passing onto a device called a slinger, 




FIGURE 1.— Product leakage from bag valve while on conveyor. 



which can be raised and lowered to a 
convenient height for the workers unload- 
ing the bags. The stackers then take the 
bags from the slinger and hand-stack them 
onto pallets. 

Except for minor effects owing to out- 
side wind currents, there is no ventila- 
tion inside these vehicles. Any dust 
generated during the conveying and load- 
ing process remains within the vehicle 
and builds to substantial levels. This 
can become a serious health problem. The 
dust generated during loading can come 
from a number of different sources; the 
two main sources are product on the out- 
side of the bag and leakage from the bag 



valve. Product on the outside of the bag 
is due to blowback (dust created as air 
and product are forced out of the bag as 
a result of excess pressure release from 
around the fill nozzle during filling); 
the "rooster tail" of product from both 
the fill nozzle and the bag valve during 
ejection from the filling machine, and 
product on the conveyor belt. Leakage 
from the bag valve occurs from movement 
on the conveyor as the bag travels to 
the loading area. This leakage can be 
substantial at conveyor transfer points 
and during the pallet loading process 
(fig. 1). 



LABORATORY-SCALE TESTING 



Laboratory-scale testing was performed 
to compare the effectiveness of a number 
of different ventilation systems in re- 
ducing the bag stackers' exposure to 
dust. Blowing systems, exhausting sys- 
tems, and a combination of both (push- 
pull systems), were tried to determine 
their effectiveness at drawing the dust 
away from the bag stacker and out of the 
vehicle. Since the time needed to set 
and maintain the ventilating system had 
to be considered so as to not interfere 
with production, only systems that re- 
quired minimal maintenance time while 
loading the vehicle were evaluated. The 
ventilation system can be set up before 
each vehicle is loaded with only minimal 
effects on production, whereas a system 
which requires changes or maintenance 
during loading has a direct effect on 
production. 

An actual railcar was used to perform 
the laboratory-scale testing. The car 
was 50 ft long, 9.5 ft wide, and 11 ft 
high (fig. 2). Wood framing covered with 
brattice cloth was used to simulate a 
full pallet of bags. On the front edge 
of each pallet, a small controlled 



quantity of tracer gas was released to 
simulate dust then mixed by a small fan 
located in front of the simulated pal- 
lets. Four sampling locations were es- 
tablished in and around the bag stacker's 
work position. To compare the various 
techniques, gas concentrations at the 
sampling points were analyzed with hydro- 
carbon analyzers. The methane tracer gas 
was allowed to build to a predetermined 
concentration of 1,000 ppm. After reach- 
ing this concentration, the ventilation 
system was turned on. The effectiveness 
of each technique was based on the gas 
dissipation rate and the baseline con- 
centration, which average concentration 
after stabilization using the system be- 
ing evaluated. This analysis was not a 
quantitative analysis that predicted an- 
ticipated dust reductions in an actual 
work situation, but was a comparison of 
the effectiveness of one system versus 
another. 

A number of fan directions and fan-size 
variations were tested with the different 
techniques. For the blowing system, air 
from the fan was directed to either the 
upper left, center, or right portion of 



SIDE VIEW 




KEY 

• Sampling location 
ACH4 release points 



Simulated 
pallets 



TOP VIEW 




Door 



FIGURE 2.— Laboratory test setup. 



the back panel of the car (fig. 3). The 
outlet was located either at raid-height 
or high in the car. In tests of the ex- 
haust system, the inlet location was 
varied from on the bottom or halfway up 
the car. In both cases, the system was 
located on the door side of the car so as 
not to interfere with the snake conveyor. 
The blowing and exhaust (push-pull) ven- 
tilating system, incorporated the blowing 
system located high in the car and the 
exhaust system located on the floor, with 
both on the door side of the car. 



Two different fan sizes were evaluated. 
The first fan had a flow rate of approxi- 
mately 2,100 cfm, which represents one 
air change per min in the half of the 
railcar being loaded with material. The 
other fan had a flow rate of approximate- 
ly 700 cfm, which represents one air 
change every 3 min. 

One technique that was tried was to use 
a curtain to block off the half of the 
railcar that was not being loaded in con- 
junction with a blowing system (fig. 3). 
This work is described in the appendix. 



SIDE VIEW 




Curtain (used only for tests 
described in the 
appendix) 



TOP VIEW 



^Right 

Center 

Left 



Door 



—Curtain 
line 



FIGURE 3.— Fan directions and location used for blowing system tests. 



LABORATORY-SCALE RESULTS 



The laboratory test results were used 
only to compare the different systems. 
Originally, the areas of interest were to 
be the dissipation of gas once the ex- 
haust system was turned on and the base- 
line concentration. However, there was 
no substantial difference in the dissipa- 
tion of gas or the decay rate from one 
system to another, so the baseline gas 
levels were used as the primary 



evaluation in comparing the systems. The 
effectiveness of the different ventila- 
tion systems decreased in the following 
order: 

1. Exhaust system over snake conveyor. 

2. Exhaust system on floor near 

pallets. 

3. Blowing and exhaust system (push- 

pull system). 



TABLE 1. - Average concentration from four sampling locations during 
laboratory testing 



Ranking 



System 
type 



Fan position 



Av cone at 


sample loca- 


tions, 


ppm 


95. 





110. 





127. 


5 


295. 





310. 





315. 





341. 


3 


345. 





372. 


5 


386. 


7 


427. 


5 


437. 


5 


450. 





510. 





532. 


5 


612. 


5 


665. 





685. 





707. 


5 


1,000. 






■L. • • • • • 

o» • • • • 

4 

5 

6 

/•••••' 

8 

9 

10.... 
11.... 
12.... 

13 

14 

15. 

16. 

17...., 
18...., 

19 

20...., 



Exhaust. . 

• • do* • • • • 

• • do* • • • • 

• • d o • • • • • 
Blowing. . 
Push-pull 

• • QO» • • • • 

Blowing. . 
••do* • • • • 
Exhaust. . 
Blowing. . 

• • do* • • • • 
• • do* • • • • 
Exhaust. . 
Blowing. . 
Exhaust. . 

. .do 

Exhaust. . 
Blowing. . 
Exhaust. . 



Center, 6-f t height, even with pallet. 

Center, 7-f t height, even with pallet 

Center, 7-ft height, 8-in back from pallet 

Floor, right, 12-in from pallet 

Roof, center 

Blower high, left, Exhaust floor, left, 2, 100-cfm 
Blower high, left, Exhaust floor, left, 700-cf m. . 

Roof, left 

Middle, left 

Floor, left, 12-in from pallet 

High, right 

High, left 

Middle, center 

Floor, left, 8 ft from door 

High, center 

Center, 6-ft height, 8 ft from door 

Floor, left, 4 ft from door 

Floor, right, 8 ft from door 

High, left, 700-cf m blower 

Floor, right, 4 ft from door 



4. Blowing system off back roof. 

5. Blowing system (high or mid-height; 

left, center, or right). 

6. Exhaust system near door (floor). 

The average baseline concentrations at 
the different sampling locations are 
shown in table 1 for each system eval- 
uated, listed in order of decreasing 
effectiveness. 

The exhaust system over the snake con- 
veyor, (at the center of the car) was 
identified as the most effective tech- 
nique and was therefore selected for fur- 
ther study. The methane release point 



was moved to the top of the pallets to 
represent dust coming from all over the 
pallet. To determine the effectiveness 
of pulling dust up and away from the bag 
stacker, the exhaust ventilation port was 
moved from being immediately above the 
front edge to 18 and 36 in past the front 
edge of the pallets. The capture effi- 
ciency increased with distance from 
slinger. Since the pallet base dimension 
is approximately 48 in square; 36 in was 
thought to be the greatest distance pos- 
sible, in order to maintain the necessary 
clearance from the back wall on the first 
pallet. 



FIELD TESTING 



The effectiveness of the exhaust venti- 
lation system located over the snake con- 
veyor was evaluated in an actual working 
environment at a mineral processing 
plant. An exhaust system was fabricated 
and installed over the snake conveyor and 
slinger. At this plant, both railcars 
and trailer trucks were loaded from the 
snake conveyor. 



To optimize the technique in the actual 
work environment, both types of vehicles 
(railcars and trailer trucks) were 
monitored for dust concentrations at 
various locations, with and without the 
ventilation system. The RAM-1 real-time 
aerosol dust monitors, built by GCA 



Corp., 4 Cambridge, MA, were used to 
evaluate respirable dust levels at var- 
ious locations during loading of the en- 
closed vehicles. The monitors use a 
light-scattering device to measure the 
dust concentration of a sample drawn in 
from the environment through a 10-mm 
cyclone. 5 

Dust was monitored at four locations 
inside the enclosed vehicles (fig. 4): 

Location 1 — On the lapel of the bag 
stacker (to give a direct reading of per- 
sonal dust exposure while stacking bags 
onto pallets). 

Location 2 — At the right side of the 
end of the slinger. This was the bag 
valve side. This location gave a direct 
reading of dust levels where the stacker 
catches the bags. 

Location 3 — At the transfer point be- 
tween the snake conveyor and the 
slinger. 

Location 4 — Over the snake conveyor, 
approximately 8 ft back from the con- 
veyor-slinger transfer point. This loca- 
tion gave a measurement of the dust 
buildup inside the main portion of the 
enclosed vehicle. 

The signal from the RAM-1 dust monitor 
was fed directly into a strip-chart 

^Reference to a specific manufacturer 
does not imply endorsement by the Bureau 
of Mines . 

^Williams, K. L., and R. J. Timko. 
Performance Evaluation of a Real-Time 
Aerosol Monitor. BuMines IC 8968, 1984, 
20 pp. 



recorder as a function of time, which 
provides the notation of the starting and 
finishing times. Any downtime associated 
with loading the vehicle was also noted 
and excluded from the dust calculations. 
Dust concentrations for each vehicle were 
calculated* A planimeter was used to 
calculate the area under the curve, which 
was then divided by the sampling time. 
This yielded dust concentration values in 
milligrams per cubic meter. 

The following factors were taken into 
account in comparing loading using the 
ventilation system with the conventional 
loading process (with no ventilation): 

Vehicle type (railcar or trailer 
truck). 

Bag size (50- or 100-lb). 

Product size (290 or 390 mesh). 

Comparisons are only made among tests for 
which these factors are identical. 

Three variations of the exhaust venti- 
lation system on the snake conveyor were 
evaluated, in each case for a 1-week per- 
iod. In each case, a 2, 100-cfm fan lo- 
cated outside of the vehicle was used. 
Flexible tubing was attached to the fan 
and extended to the snake conveyor sling- 
er transfer point. The systems differed 
as follows: 

Test 1: The flexible tubing was con- 
nected to a section of 10-ft-long, 
12-in-diam rigid fiberglass tubing that 
extended past the end of the slinger by 



Snake 
conveyor 




FIGURE 4.— Dust monitoring locations used for field evaluation. 




FIGURE 5.— Ventilation system used for test 2. 



approximately 3. 5 ft. The bottom of the 
tubing was 6. 5 ft above the floor, which 
allowed the bag stackers to perform their 
job without interference. 

Test 2: The flexible tubing was con- 
nected to a special transition composed 
of two 8-in-diam outlets (main exhaust) 
and one 6-in-diam outlet (transfer point 
exhaust). The two 8-in lines ran under 
the slinger, on either side of the dis- 
charge. The 6-in line was extended to 
the bag valve side of the snake conveyor- 
slinger transfer point to capture the 
dust generated at this point (fig. 5). 

Test 3: As in test 1, the flexible 
tubing was connected to 12-in diam rigid 



fiberglass tubing that extended up and 
out past the bag slinger. Six-inch-diam- 
eter tubing was extended to the bag valve 
side of the snake conveyor-s linger trans- 
fer point, as in test 2 (fig. 6). 

Every enclosed vehicle loaded during 
the test period was monitored, although 
there was no control with respect to the 
vehicle type, mesh size, or bag type; 
these were based on customers' orders. 
The first vehicle was monitored without a 
ventilation system. When a vehicle was 
ready to be loaded with an identical 
load, the exhaust ventilation system was 
installed. 




FIGURE 6.— Ventilation system used for test 3. 



10 



Table 2 gives the average respirable 
dust concentration with the system off 
and on at the various sample locations, 
and the percent dust reduction for load- 
ing an entire vehicle. The values were 



measured only during actual work periods, 
and therefore they were higher than nor- 
mal for a worker's eight hour exposure 
level, that includes break periods and 
times when the system is not operating. 



TABLE 2. - Dust reductions of field testing exhaust ventilation system 



Vehicle and product size 



Monitoring 
location 



Dust cone, mg/m 3 



Off 



On 



Reduction in dust 



cone 



pet 



TEST 1 



Railcars 
290 mesh, 100-lb bags. 

Trailers 
290 mesh, 100-lb bags. 

390 mesh, 100-lb bags. 

390 mesh, 50-lb bags.. 

Railcars 
390 mesh, 100-lb bags. 

Trailers 
290 mesh, 100-lb bags. 



Stacker 

Slinger 

Conveyor. 

Stacker 

Slinger 

Stacker 

Slinger 

Conveyor. . . . . 

Stacker 

Slinger 

TEST 2 

Stacker 

Slinger 

Transfer 

Stacker 

Slinger 

Transfer 

Conveyor 

Stacker 

Slinger 

Transfer 

Conveyor 

TEST 3 

Stacker 

Slinger 

Transfer 

Conveyor 

Stacker 

Slinger 

Transfer 

Conveyor 



2.47 
1.38 
2.40 

2.04 
2.08 

1.51 
1.69 
1.52 

1.53 
1.48 




68.4 
63.8 
88.3 

63.2 
71.2 

49.0 
63.9 
84.2 

1.9 
■148.6 



390 mesh, 100-lb bags. 



3.54 
1.50 
1.61 

3.49 
2.64 
1.82 
1.64 

1.66 

1.48 

1.17 

.94 



1.46 

1.07 

.82 

1.61 

1.10 

.71 

1.07 

1.33 

1.07 

.52 

.61 



58.8 
28.7 
49.1 

53.9 
58.3 
61.0 
34.8 

19.9 
27.7 
55.6 
35.1 



Trailers 
390 mesh, 100-lb bags. 



390 mesh, 50-lb bags. 



1.76 
1.38 
2.07 
2.80 

4.02 
4.04 
6.58 
4.28 



0.34 
.45 
.43 
.42 

1.38 

1.42 

.76 

.24 



80.7 
67.4 
79.2 
85.0 

65.7 

64.9 
88.5 
94.4 



11 



DISCUSSION 



The intent of the laboratory-scale 
testing was to establish conditions that 
would be representative of actual field 
conditions and select the most effective 
system for field testing. The factor 
that was not simulated during laboratory- 
scale testing, but which proved to be 
significant during the field evaluation 
was the dust emitted from the bag valve 
at the snake conveyor-slinger transfer 
point. Any dust that was emitted at this 
point was drawn over the stacker to the 
exhaust ventilation inlet in front of the 
stacker (test 1). This can be seen from 
the railcar (290-mesh, 100-lb bag) and 
trailer truck (390-mesh, 100-lb bag) re- 
sults. The dust reduction at the stacker 
and slinger locations was not nearly as 
good as the dust reduction at the convey- 
or location. Since the conveyor sample 
location was behind the transfer point 
dust source, it was not affected. 

The amount of dust liberated at the 
snake conveyor-slinger transfer location 
increased with the 50-lb bags. The 50-lb 
bag results in test 1 showed no dust re- 
duction at the stacker location and an 
increase in dust at the slinger location. 
The increase in dust measured at the 
slinger location can be attributed to the 
fact that the dust generated at this 
transfer location flowed directly over 
the slinger monitor as it was drawn to 
the exhaust ventilation system. 

Because of the dust at the bag valve 
side of the snake conveyor-slinger trans- 
fer point, a small exhaust port was ex- 
tended to this location in test 2. The 
two 8-in-diam main exhaust lines were 
routed under the slinger because this 
would have been a more advantageous per- 
manent location for the system. Visual 
observations and actual dust measurements 



both showed the small transfer point ex- 
haust port to be effective in capturing 
the dust, with an average reduction of 
55 pet. The main exhaust was not as ef- 
fective as in the first system because 
the inlet underneath the slinger was not 
powerful enough to pull the dust from the 
pallet stacking location along the floor 
and away from the bag stacker position. 

The final and recommended design (test 
3) incorporated the exhaust system ex- 
tended over the pallets to capture the 
dust generated during bag loading. Vis- 
ual observation showed that this system 
was very effective in capturing the dust 
that rose above the pallets during the 
stacking process. The small transfer 
point exhaust port was also used because 
it was effective at capturing the dust 
generated from the bag valve, which was 
shown to be a substantial dust contribu- 
tor in test No. 1. The dust reductions 
achieved with this final version ranged 
from 65 to 95 pet at all sampling loca- 
tions. These reductions are substantial, 
considering that a 2, 100-cfm fan was 
used, which changed half the air in the 
railcar and trailer truck in 1 min. It 
is obvious that the use of a larger fan 
would increase the efficiency of the sys- 
tem. However, the added efficiency would 
have to be weighed against the accompany- 
ing increase in capital and operating 
costs. 

It is anticipated that a mineral pro- 
cessing plant, that installs a system 
similar to the one recommended here, as a 
permanent dust control technique, would 
run the exhaust into a baghouse dust col- 
lector. The only constraint on the sys- 
tem would be size of the tubing to be 
located under or over the snake 
conveyor. 



12 



COST CONSIDERATIONS 

The evaluated exhaust ventilation sys- dust pulled from the vehicles, some type 

tem required minimal capital and operat- of filtration system might be necessary, 

ing costs. The approximate cost of the About 8 worker hours were required to set 

system was as follows: up the system. 

It required from 5 to 10 min to install 

2,200-cfm vane axial fan, 5-hp the exhaust ventilation system into each 

motor $2,200 enclosed vehicle before loading could be- 

60 ft of 12-in-diam flexible gin during the field evaluations. Since 

tubing 450 there is always a down time between the 

10-ft length of 12-in loading of each vehicle, this did not af- 

fiberglass tubing 80 feet production. As the vehicle was 

Bracket to attach to snake loaded and the snake conveyor was con- 
conveyor 200 tinually backed out of the vehicle, 

Additional minor supplies 100 brackets and tubing were removed from on 

Total 3,030 top of the snake conveyor to avoid a 

clearance problem with the mill building. 

The only operating cost was the power For actual use in a plant, a more perma- 

needed for the 5-hp motor necessary to nent installation could be developed. It 

drive the fan. If the system is used in did not appear in the Bureau's interest 

conjunction with a baghouse system, the to pursue a more permanent installation 

incremental cost to operate the baghouse or a deployment system since every plant 

would also have to be considered. If a would require its own design, 
baghouse is not available to filter the 

CONCLUSIONS 



The exhaust ventilation system de- 
scribed in this report effectively lowers 
respirable dust concentrations when bags 
of product material are loaded directly 
into enclosed vehicles by workers. The 
final and recommended design exhausts 
about 2,000 cfm through a 12-in-diam tube 
located 3.5 ft in front of the slinger at 
a height of 6.5 ft. A small exhaust tube 
is used at the bag valve side of the 



snake conveyor-slinger transfer point to 
capture the dust generated at this loca- 
tion. When this system was used during 
loading, respirable dust reductions 
ranged from 65 to 95 pet in both railcars 
and trailer trucks. The system involves 
minimal equipment, installation, and op- 
erating costs, and can be modified by 
mineral processing plants for permanent 
installation at individual operations. 



APPENDIX. — CURTAIN EVALUATION 



13 



The technique of using a curtain ar- 
rangement to block off the half of a 
railcar that was not being loaded was 
evaluated. A brattice mining cloth was 
attached to two 5-ft-long pieces of 2- by 
4-in lumber. Using extender poles to 
secure the 2 by 4's to the ceiling, a 
simple and effective curtain barrier was 
installed in a matter of minutes. The 
curtain was designed to improve ventila- 
tion by preventing the airflow from 
traveling back into the half of the car 
that was not being loaded. A barrier 
curtain would only be applicable with 
blowing ventilation systems when loading 
railcars. 

Tests were performed comparing the 
effectiveness of different blowing 



ventilation systems with and without the 
curtain. The results showed that use of 
the curtain barriers produced no measur- 
able difference in methane tracer gas 
concentrations. Table A-l shows the 
average methane tracer gas concentration 
for the four sampling positions and the 
percent reduction in methane tracer gas 
levels with the curtain in place. There 
was a 4-pct increase in the gas concen- 
tration measured at the stacker location 
with the curtain in place when the re- 
sults were averaged together, but it is 
believed that this increase was due 
mainly to sampling error. 



TABLE A-l. - Effect of blowing ventilation system 
with and without curtain 



Fan position 


and 


curtain 


Av cone, 


ppm 


Change, pet 


High, left: 


437.5 
585.0 

532.5 
492.5 

427.5 
377.5 

372.5 
397.5 

450.0 
451.3 




With 


-33. 7 


High, center: 




With 


7.5 


High, right: 




With 


11. 7 


Middle, left: 




With 


-6. 7 


Middle, center: 






-.3 



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